Nutrient Testing

The following section outlines the types and frequency of samples that must be obtained for your farm Plan, as well as guidelines on how to take good, representative samples.

NOTE: THE PRODUCER IS RESPONSIBLE FOR TAKING ALL SAMPLES AND FOR MAINTAINING ALL RECORDS FOR A PERIOD OF AT LEAST 5 YEARS.

TESTING SUMMARY POINTS

Testing Requirements:

Soil tests will be used as the basis for nutrient application. Each field or management unit shall be tested for pH, EC (where appropriate), OM, nitrate-N, ammonium-N, P (Bray P1), and K every three years. Collection and handling of soil samples shall comply with Cooperative Extension procedures and protocols.

A Pre-sidedress Nitrate Test (PSNT) shall be performed on corn ground prior to fertilizer sidedress and/or manure irrigation and top dress applications.

Annual post-harvest soil nitrate tests shall be taken in the fall in each field according to procedures outlined in the OSU Extension publication, Post-harvest Soil Nitrate Testing for Manured Cropping Systems West of the Cascades.

Manure shall be tested at least three times annually (spring, summer, fall). If manure is applied from more than one waste storage pond, a sample shall be taken from each. At least one test shall be a laboratory analysis; the others may be on-farm tests using a hydrometer or nitrogen meter. The lab manure test shall include analysis for total nitrogen, ammonia nitrogen, phosphorus, and percent moisture. Testing for K, Ca, S and Mg is recommended, but not required. It is recommended that manure be tested at or prior to application.

Forage testing and determination of crop yield are highly recommended. A minimum test should include: percent moisture, and crude protein for each harvest. Testing for fiber (ADF, NDF, CF and Lignin) and minerals, especially potassium, is also recommended.

If applicable, irrigation water shall be applied in accordance with an irrigation water management plan. Records of water application should be maintained.

All test results shall be maintained with application records.

For more details on testing, see specific testing sections below.

NUTRIENT TESTING

TESTING PROTOCOL

Soil Testing

Frequency. Soil tests are used as the basis for nutrient application, and should be available for each of your fields where crops are grown and fertilizer (manure) is applied. At a minimum, each field or management unit should be comprehensively sampled once as a baseline. This will help establish an average for the field and identify any areas of variation that may require different nutrient requirements. After a baseline is achieved, testing may be conducted once every three years thereafter as a minimum. More frequent testing will aid in better agronomic application rates. If manure is going to be applied to your field, an annual fall nitrate test should be taken to a depth of 12 inches on all fields after harvest in the fall.

Analysis. Soil samples should be analyzed for: pH, EC, OM, nitrate-N, ammonium-N, P (Bray), and K. Additional tests may be required for various practices. For instance, a Pre Sidedress Nitrate Test (PSNT) shall be performed on corn ground prior to each sidedress application.

Manure Testing

Frequency. Manure must be tested at least three times annually (spring, summer, fall). Manure should be tested prior to application on fields to determine the nutrient content. Due to the heterogeneity of manure lagoons, manure samples can be extremely variable. Agitation prior to sampling is recommended, as are more frequent samples throughout the year.

Analysis. At least one of your three annual tests should be a comprehensive laboratory analysis. The other two tests may be on-farm tests using a hydrometer or (Agros) nitrogen meter. The lab manure test shall include analysis for total N, ammonia nitrogen, and percent moisture. Testing for P (Bray), K, Ca, S, and Mg is recommended but not required on a regular basis.

ANALYTICAL LABORATORIES

Make sure to send samples to an accredited laboratory for analysis. Call or go online to check for laboratory sampling requirements, analysis available, and prices prior to sending in your samples. Some local (drop off locations) and comprehensive laboratories are listed below. Refer to Heading V, Section 12 for a list of more laboratories in the North West.

INTERPRETING YOUR RESULTS

Once you have your comprehensive and/or fall nitrate soil results, comprehensive manure results, and irrigation nitrate results, it is time to interpret what they all mean. Analyses of your results will aid you in adjusting your nutrient balance and agronomic application rates on an ongoing basis. Creating graphs and will help you track your nutrient balances over time.

HOW TO TAKE A SAMPLE

The challenge of crop nutrient management is to balance production and economic optimization with environmental impacts. Successful crop production is dependent upon effective nutrient management that includes identifying nutrient deficiencies and excesses and balancing nutrient inputs and crop removal outputs. Obtaining a good soil, manure, or water sample is imperative for accurate analysis and calculation of crop needs and agronomic application rates. The following guidelines outline proper technique for obtaining samples as well as handling and transport.

Soil Sampling

Field sampling and soil testing has become an important tool for assessing soil fertility and arriving at proper manure application rate recommendations. It’s also a valuable management aid for studying soil changes resulting from cropping practices and for diagnosing specific cropping problems. Soil testing provides an index for the nutrient availability in soil and is a critical step in nutrient management planning. Proper soil sampling will provide accurate soil test results and reliable nutrient recommendations. Soil sampling technique, timing of sampling, and type of analysis all need to be considered for accurate results. A good, representative soil sample should be taken for every field that manure is applied to.

Collection and handling of soil samples shall comply with Pacific Northwest Land Grant University (Cooperative Extension) procedures and protocols. See Sampling Guidelines below as well as the Reference Materials in Heading V, Section 12 for more information on soil testing and interpretation.

When you should sample. Cultivated fields for spring seeding should be sampled after October 1. These fields can also be sampled in the spring, but time may be limited by then. Fields for fall-seeded crops should be sampled one month before seeding. Forage fields for seed, pasture, or hay may be sampled after September 1. Problem soil areas may be sampled anytime. Frozen and waterlogged soils should not be sampled because of the difficulty in obtaining a representative sample.

Where you should sample. Soil variability is a major concern when deciding how to collect a representative soil sample. Soil samples submitted for analysis should be representative of the field or portion of a field. Therefore, by sampling from an area of the field where yield is typically average, soil test results should come back with an average representation of the field. Identifying areas that are representative can be difficult without a first hand knowledge of the field. If the person taking the soil samples does not take the time or have the knowledge required to take a sample in the appropriate location, the results can come back somewhat sporadic.

Benchmark sampling is recommended for fields with no prior nutrient analysis. A small area (generally about ¼ of an acre) representing the majority of the field is sampled the same number of times as in random sampling (15-20 samples). This is the reference area from which fertilizer recommendations are made. The benchmark site should be marked with a global positioning system (GPS) or other means so that one can return there for subsequent years sampling. Sampling from the same area will reduce sampling variability to create a better picture of year-to-year changes. More than one benchmark is recommended if you cannot identify a dominant production area on your field.

After a benchmark has been established, sampling should be conducted every 3 years. There are a few types of field sampling methods that can be conducted, but random and managed random sampling are the most common. Random soil sampling is the traditional approach that works for uniform fields with little variation. In this case, you would take 15-20 samples located across the entire field. This would provide an average picture of the entire field. Managed random sampling technique samples from areas identified as “average” production areas. This method is recommended if you have spots of variability in production across your field, and want to only represent the typical or average parts of the field. In this case, you would take 15-20 random samples only from the areas of the field that have a “typical” production rate.

Each field must be sampled separately. Size up each field and observe variations in yield and crop growth, texture, color, slope, degree of erosion, drainage, and past treatment. Sizable areas of fields where growth is significantly different from the rest of the field should be sampled separately. Avoid unusual areas such as dead or back furrows, old straw, hay or manure piles, waterways, saline spots, eroded knolls and old fencerows. Dividing a field into management zones based on production rates allows for an understanding of different conditions within a field. This is particularly effective in rolling and variable landscapes. For example, a large depression may be a very productive area, but a separate soil test may indicate it can be optimized with a higher rate of nitrogen than the benchmark is indicating. While most producers do not have variable rate capabilities on manure application equipment, rates can often be easily increased through other adjustments.

How you should sample. First, select 15 to 20 sampling sites representative of the portion of the field to be tested. Second, take each sample in the same exact fashion as the last to ensure there is limited or no human induced variability between samples. A variety of sampling tools are available to collect soil samples. They range from a spade to hydraulic powered coring equipment. Representative soil samples can best be obtained by using a core-sampling tool. Take soil core samples down to at least 12 inches at each of the 15 to 20 sampling sites. For improved nitrogen and sulfur evaluation or where problem soils are encountered, separate samples should be taken from varying depths at the same 15 to 20 sites and analyzed separately.

Sample handling and storage. Preparing samples for laboratory analysis is just as important as collecting the soil sample. Place all sample cores in a clean pail or bag and mix them thoroughly, crushing lumps in the process. Remove a well-mixed, homogeneous sub-sample of that mixture and place it in a clean airtight bag. Write sample identification information (e.g., date, field #, etc.) on the bag. Store the sample in a cool, dry location and send to the laboratory within 12-24 hours of sample attainment. Samples can also be stored in a refrigerator for a couple of days or frozen if sample delivery is delayed. Provide complete information for each soil sample on the sheet supplied by the lab. Where unusual problems exist, these should be noted in detail. Keep a completed field plan of the area represented by each sample for your own records.

Manure Sampling

Laboratory analysis of manure nutrient content is an essential component of crop management planning that can improve farm profitability and the environment. Manure analysis is also necessary for application rate planning. Estimates of manure nutrient content are available from a number of published sources, but nutrient composition varies widely between farms due to differences in animal species and management, and manure storage and handling. The only method available for determining the actual manure nutrient content for your particular operation is with laboratory analysis. Since such a small amount of material is used for analysis, it is essential that the sample submitted represent the manure that is applied to the fields. The following guidelines outline proper technique for obtaining samples as well as handling and transport.

When you should sample. Liquid manure samples can either be taken at hauling time, or directly from the waste lagoon. For safety and best results, it is recommended that manure be sampled during hauling. The sample will be more accurate because it has been mixed and safer to obtain. The only drawback to using this method is that the results of this year's sample cannot be used to plan this year's manure applications. This is because samples are taken during application periods and lab results can take up to a week to be returned. Additionally, manure results will vary throughout the year as dilution or nutrient influx occurs. However, manure test results can be used to adjust application rates made later in the year and estimate next year's manure nutrient content, if all variables (i.e., cow numbers, rainfall, inflow sources, etc.) stay relatively the same.

For systems that are emptied or cleaned out once per year, a good rule of thumb is to sample and analyze manure each time it is applied. This is especially true for uncovered lagoons, pits, basins, and stacking slabs. Variations in temperature and precipitation between years will affect changes in nutrient content due to dilution, evaporation, leaching, and volatilization. Manure from under-barn concrete pits or covered above ground tanks will not vary as much between applications, unless the type of animal or other factors change (i.e., species, size, feed, bedding, confinement). Systems emptied twice per year or more may differ between application times, so a fall analysis may not be accurate for planning spring applications.

Sampling and handling from tanker truck. For best results, sample the manure that is in the tank or spreader box being delivered to the field for application. Such samples will be the most representative because the liquid manure is likely to have been agitated in order to load the tank, and semi-solid manure scraped from the barn is moderately mixed after being loaded into a box spreader. Ideally, the sample submitted for lab analysis should be a mixture of manure taken from several loads (5-10) representing the beginning, middle, and end of the application process. This will help ensure that manure samples accurately represent the manure being applied.

For liquid manure, retrieve samples with a plastic pail or a coffee can on a pole from the top of the spreader if possible. Otherwise, a sample can be taken from the bottom unloading port. Sampling should be done immediately after filling. After collecting 5-10 sub-samples in a 5-gallon bucket, mix sub-samples thoroughly. From this mixture, fill a clean/sterile sample jar 3/4 full (allowing room for gas expansion), wipe off sample jar, and seal in a bag. Be sure to write the date, sample number, and any other pertinent information on the jar. Manure samples should be stored in a cool, dark place and sent to the laboratory within 12-24 hours of collection. If this is not possible, samples should be frozen prior to mailing in order to slow down any microbial activity, and mailed early in the week so that they will not remain in the post office over the weekend.

Sampling and handling from a storage lagoon. An alternative to sampling manure during application is to sample manure from the storage structure prior to application. However, sampling from storage lagoons is not as accurate as sampling during application, and it can be more dangerous. For these reasons it is recommended that manure be sampled during application. If time and management practices prevent this, manure can be sampled from the storage structure.

Lagoon samples should be taken with a plastic pail or a coffee can on a pole from varying locations and depths of the lagoon. If a can or other container cannot be attached to a long pole and dipped into the pit or basin, an alternative method is to use a 1/2" or 3/4", 8-10-ft. PVC pipe. Push the pipe into the manure, avoiding the bottom foot of the structure. Place a hand over the top opening to seal the pipe, pull up, and empty into a bucket. Do not collect samples from areas that have uncharacteristic crusts or floating chunks on the surface. Collect anywhere from 10-20 sub-samples in a 5-gallon bucket, mix sub-samples thoroughly. From this mixture, fill a clean/sterile sample jar 3/4 full (allowing room for gas expansion), wipe off sample jar, and seal in a bag. Be sure to write the date, sample number, and any other pertinent information on the jar. Manure samples should be stored in a cool, dark place and sent to the laboratory within 12-24 hours of collection. If this is not possible, samples should be frozen prior to mailing in order to slow down any microbial activity, and mailed early in the week so that they will not remain in the post office over the weekend.

Solid manure sampling. Stacked, piled, or bedded pack manure can also be sampled in storage, and an average nutrient content estimated. Using a pitch fork or shovel, take 10-20 sub-samples from different depths and locations in the pile or pack. Place the sub-samples in a pile, mix, and place a composite sub-sample of the pile (avoid large pieces of bedding) into a large airtight bag. You may want to take two or more composite samples for analysis, and use the average of the results. Write the sample number, date, and other pertinent information on the bag.

Keep track of all manure analyses from a particular storage system over a period of time. This will help you determine both the necessary frequency of sampling and an average nutrient content to use for manure application planning. Remember that manure should always be resampled if you change any component of your animal management or manure storage or handling system.

Water Sampling

A sample of well water should be taken prior to irrigation if there is concern over nitrate levels in the water. Nitrate can be a contributing source of nitrogen fertilizer and may offset agronomic rates. The sample can be taken directly from the well or at various points during irrigation. Collect the sample into a sterile container, store in a cool place, and send to the lab within 24 hours of sampling.